The invention relates to the art of semiconductor manufacture. It finds specific application for fuses within an integrated circuit and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to PROM-type devices, trimming resistors and other like devices.
Fuses have long been important circuit elements. While fuses are generally used for circuit protection and fire prevention, in integrated circuits they are also used as a means of calibration, programming and providing data security. For example, fuses can be used for trimming or calibrating certain parameters in a circuit, or for recording information by selectively blowing fuse elements in an array, or for preventing information stored in a memory device from being accessed. Whether the fuse exists for circuit protection or to achieve certain operating parameters the fuses are designed to change state under certain conditions. Indeed, one way to change state is a to blow a fuse. This is accomplished by applying a sufficiently high current through the fuse. The heating that results causes the conductor to melt or vaporize. In this way, the fuse is transformed from its conductive state to a blown, or open circuit state.
The conductors used to fabricate fuses on integrated circuits are made of layers of conductive metal, typically aluminum or aluminum compound. For reasons unrelated to fusing, the aluminum layer is deposited over a barrier layer typically comprising titanium and/or a titanium compound . Unfortunately, the addition of titanium has an adverse effect on fuse reliability. The adverse effect is caused by the high melting point of titanium as compared to the aluminum bulk conductor layer. Thus, when current levels are applied to the metal stack which should effect a blown fuse, sometimes portions of the barrier layer remain. This remaining portion of the barrier provides a conductive path around the xe2x80x98blownxe2x80x99 fuse. In other words, current levels that do melt the bulk conductor sometimes do not completely melt the barrier layer. This partial path undesirably allows a current path, defeating the intended open circuit.
Accordingly, it is desirable to provide a technique for manufacturing a more reliable fuse, using existing methods of applying the metal stack.
The present invention contemplates a new and improved method and apparatus fuse overcomes the above-referenced problems and others.
In accordance with one aspect of the present invention, a circuit element which interrupts electrical conductivity in a portion of a circuit includes a first layer providing adhesion for the circuit element. A trench is also provided in the first layer and a second layer, overlaying the first layer, has an interruption in the trench. A third layer including electrically conductive material, overlays the second layer.
In accordance with another aspect of the present invention, the trench defines a volume in the first layer bounded by an opening in the first layer, an undercut area in communication with the opening, and a bottom floor. The bottom floor is larger than the opening in the first layer.
In accordance with another aspect of the present invention, the first layer includes an overhang which shields the portion of the bottom floor of the trench.
In accordance with another aspect of the present invention, the circuit element further includes a weak spot in the third layer adjacent to the interruption.
In accordance with another aspect of the present invention, the weak spot includes an area of reduced mechanical strength resulting from a lack of structural support by the second layer in the area of the interruption.
In accordance with another aspect of the present invention, the weak spot includes an area of reduced mechanical strength in the third layer resulting from crystalographic changes within the third layer in the trench.
In accordance with another aspect of the present invention, the second layer includes conductive material, and the weak spot includes an area where electrical communication is only provided through the third layer.
In accordance with another embodiment of the present invention, in an integrated circuit fuse including an electrical conductor having a reduced cross sectional area in a first preweakened area, the fuse includes: an undercut trench on top of a dielectric layer, and a second preweakened area in the electrical conductor adjacent to the trench.
In accordance with another aspect of the present invention, the fuse further includes a barrier layer applied to the dielectric layer with at least one gap. The electrical conductor is applied over the barrier layer and over the gap so as to create a fuse with a second preweakened area being adjacent to the gap.
In accordance with another aspect of the present invention, the barrier layer includes a layer of titanium or a titanium compound and the electrical conductor includes a layer of aluminum or an aluminum compound.
In accordance with another aspect of the present invention, the fuse further includes a barrier layer disposed between the dielectric layer and the metal layer, where the barrier layer has a discontinuity in the void.
In accordance with another aspect of the present invention, the weak point includes a mechanical weakness from the discontinuity in the barrier layer.
In accordance with another aspect of the present invention, the weak point includes an electrical weakness from the discontinuity of the barrier layer in the neck down region of the metal layer adjacent to the void.
In accordance with another aspect of the present invention, the void includes an undercut which shields a portion of the bottom floor by an overhanging edge of the top opening during application of the barrier layer. The overhanging edge establishes the discontinuity in the barrier layer.
In accordance with another aspect of the present invention, the undercut includes an acute angle between a side wall and the bottom floor of the dielectric.